I. Field of the Invention
The present invention relates to an improvement in a V-belt type continuously variable transmission and, more particularly, to a V-belt type continuously variable transmission which is equipped with a torque responsive mechanism exhibiting excellent torque and speed response characteristics.
II. Description of the Prior Art
Generally speaking, snowmobiles commonly use a V-belt type continuously variable transmission. Such a transmission is generally constructed to include a drive pulley and a driven pulley, each of which is composed of a fixed sheave or pulley half fixed in the axial direction and a movable sheave or pulley half which is movable in the axial direction. A V-belt joins the drive pulley and the driven pulley. Moreover, as is disclosed in the Teal U.S. Pat. No. 4,023,635, the V-belt type continuously variable transmission is equipped with a speed responsive mechanism associated with the drive pulley and a torque responsive mechanism associated with the driven pulley so that it can continuously vary the shift ratio between the drive and driven pulley in relation to the drive speed and driven torque. When the torque load upon the driven shaft is increased with the increase in the load upon the drive track, as when the snowmobile runs uphill, the aforementioned torque responsive mechanism transmits an axial force matching that increase from the driven pulley to the drive pulley so that a satisfactory shift ratio may always be attained.
In the aforementioned Teal U.S. Pat. No. 4,023,635, the torque responsive mechanism is comprised of inclined cam surfaces which are opposed to one another and positioned between a spring cap, which is fixed to the movable sheave or pulley half, and a fixed sheave or pulley half. Those opposed inclined cam surfaces are moved in the axial direction relative to each other by the torque loaded upon the driven shaft, while the pulley halves are sliding and turning relative to each other. Hence, the aforementioned movable sheave is moved closer to the fixed sheave by the relative movement caused by the cooperating cam surfaces. As the two sheaves are removed closer together, the effective diameter of the driven pulley is increased and the effective diameter of the drive pulley is decreased so that the torque to be transmitted from the drive pulley to the driven pulley is increased.
The prior art torque responsive mechanism, as represented by the Teal U.S. Pat. No. 4,023,635, has a significant drawback in that it exhibits a high frictional resistance when the opposed inclined cam surfaces move relative to each other. As a result, even if torque fluctuations are imposed upon the driven shaft, because of that frictional resistance, the relative movements of the inclined cam surfaces do not occur simultaneously with those torque fluctuations, but instead a noticeable time lag occurs. Hence, the torque responsive mechanism of the prior art suffers from poor torque response characteristics when torque fluctuations occur on the driven shaft. Another defect of the prior art arrangement is that the torque responsive mechanism has poor speed response characteristics to acceleration or deceleration of the engine. As such, it cannot control the desired engine speed with smoothness and precision.